The present invention concerns a device for fastening a steering wheel to a steering column, transmitting both torque and axial forces without play, whereby the end of the column and the hub of the wheel are designed to ensure form-fit transmission of torque at the site of their engagement.
Steering wheels are usually fastened to steering column by means of a conical component, serrations, and an outer thread at the upper end of the column and of another conical component and further serrations at the hub of the wheel. The wheel is mounted on the column at the correct angle and tensioned axially to the column with a nut such that the force fit deriving from the conical component is sufficient to transmit any torque that normally occurs. The serrations, the means of transmitting the torque form-fit, that is, only come into play when the force-fit connection is overloaded, in the event of an accident for example, or when the self-locking axial threaded connection would come loose.
Since no form-fit connection for the transmission of torque from a steering wheel to a steering column entirely without play that can be assembled at a justifiable expenditure and since such play is covered by manufacturing-dictated tolerances, it is the force-fit and not the form-fit components that must be relied on for the transmission of torque between the wheel and the column. The former, however, are not considered intrinsically adequate and must be augmented with form-fit components.
The aforesaid fastening methods assume that the steering wheel hub will be accessible from the front so that the nut can be screwed over the steering column. More and more vehicles are, however, being manufactured on an industrial scale with at least a driver's-side airbag that must be accommodated in the wheel, and the airbag module can generally be installed only once the wheel has been mounted on the column. This is not only relatively complicated, but also leads to fabrication problems, in that the airbags are sometimes installed not by their manufacturers or by the wheel manufacturers but only during final assembly of the motor vehicle. Furthermore, there is an increasing trend to produce steering-wheel covers as far as possible in one piece, leaving no way of fastening the wheel to the column by the aforesaid procedures.